diff --git a/setup.sh b/setup.sh
index 2efdc92..c0f441b 100644
--- a/setup.sh
+++ b/setup.sh
@@ -88,13 +88,14 @@ then
   error
 fi
 message "check sources.list"
-if ( ! grep "contrib" /etc/apt/sources.list > /dev/null ) && ( ! grep "non-free" /etc/apt/sources.list > /dev/null )
+if ! ( ( grep "contrib" /etc/apt/sources.list > /dev/null ) && ( grep -E " non-free( |$)" /etc/apt/sources.list > /dev/null ) )
 then
-  message warn "'contrib' and 'non-free' not in your sources.ist, i will deploy my own"
+  message warn "I need 'contrib' and 'non-free' in sources.ist, i will deploy my own"
   confirm_continue
-  message "backup old sources.list"
+  message "backup old sources.list to /etc/apt/sources.list.bak"
   sudo cp /etc/apt/sources.list /etc/apt/sources.list.bak
-  echo "deb http://deb.debian.org/debian/ bookworm main contrib non-free non-free-firmware
+  cat << EOF > /etc/apt/sources.list
+deb http://deb.debian.org/debian/ bookworm main contrib non-free non-free-firmware
 deb-src http://deb.debian.org/debian/ bookworm main contrib non-free non-free-firmware
 
 deb http://security.debian.org/debian-security bookworm-security main contrib non-free non-free-firmware
@@ -104,7 +105,8 @@ deb-src http://security.debian.org/debian-security bookworm-security main contri
 # see https://www.debian.org/doc/manuals/debian-reference/ch02.en.html#_updates_and_backports
 deb http://deb.debian.org/debian/ bookworm-updates main contrib non-free non-free-firmware
 deb-src http://deb.debian.org/debian/ bookworm-updates main contrib non-free non-free-firmware
-" | sudo tee /etc/apt/sources.list
+EOF
+
   message "apt update"
   sudo apt update
 fi